This invention relates generally to semiconductor device manufacturing, and more particularly to methods and structures for transmitting heat away from semiconductor dies using conductive heat spreaders.
Semiconductor circuit processing has seen a dramatic improvement in lithography that allows semiconductor manufacturers to shrink the size of circuits formed on wafers. This shrinkage has a cost advantage for the manufacturer in that circuit density is increased because more circuits can be formed within a given area of a wafer surface. A known drawback to increased circuit density, however, is an increased need for power dissipation. Semiconductor circuits are not perfect conductors and their operation necessarily generates a lot of heat caused by a resistance to the electricity running through the circuits. The amount of heat generated within a given area increases as circuit density increases. Heat buildup within the circuit can cause failures. Accordingly, more complicated power dissipation schemes have been developed to draw heat away from the circuits that generate it.
One known method for addressing this power dissipation problem is to use an integrated heat spreader (IHS). In these known systems, an IHS is coupled to a semiconductor die using a thermal interface material (TIM) so that heat generated within the die is conducted through the TIM and thence to the IHS where it is then radiated away from the die. Current state of the art processes for bonding the IHS to the die involve using a flux and soft solder preform around 200 μm as the thermal interface material. These methods have severe limitations, however, as circuit size decreases and circuit density increases. Both full thickness silicon die (˜775 microns) and the thick solder TIM (˜200 microns) contribute significantly to the total thermal barrier and thus increase the junction temperature and lower reliability. Soft solder-based thermal interface materials cannot bond the die to the IHS reliably if the TIM thickness is small. Furthermore, TIM bonding with fluxes generates voids thereby causing reliability issues. And although fluxless bonding methods are known, these known methods have low throughput and involve high costs thus making them unsuitable to high volume semiconductor manufacturing.
Accordingly, the need exists for an alternate method for bonding dies to integrated heat spreaders that overcomes the drawbacks of known prior art methods.